Diffusion transfer photographic elements comprising 5-hydroxy-4-azabenzimidazole and a second azabenzimidazole,and processes for their use

ABSTRACT

A NOVEL COMBINATION OF AZEBENZIMIDAZOLES IS USED FOR THE PREVENTION OF FOG FORMATION IN DIFFUSION TRANSFER PHOTOGRAPHIC PROCESSES, WHICH COMBINATION RESULTS IN A DYNAMIC RANGE EXTENSION OF THE PHOTOGRAPHIC SYSTEM.

'Aug. 29, 1972 J.D.GONDOLFE ETAL 3,687,660

DIFFUSION TRANSFER PHOTOGRAPHIU ELEMENTS COMPRISING b-HYDROXY-L-AZABENZIMIDAZOLE AND A SECOND AZABENZIMIDAZOLE, AND PROCESSES FORTHEIR USE Filed Oct. 15, 1970 4 l3 o E DEVELOPER LAYER /////////////7 l5e-|NTERLAYER H 1e /////////////7-MAGENTA DYE DEVELOPER LAYER 2Sheets-Sheet 1 E2EE'.85"EE /////////////)+-INTERLAYER I L YELLQW DYEDEVELOPER LAYER 2o /////////////7 ERLESEEN ELQF? A AUXILIARY LAYER 23//////////jlmAss-Rscelvme LAYER 22 24 ESPACER 2s////////////}Y-NEUTRAL|ZING LAYER as FlG.l

INVENTORS JAMES D. GONDOLFE ,und RUTH SEANLAN an JEANNE AWARD (horn n.rung. 7?"14/1'0 ell/run 811410411111 ATTORNEYS Aug. 29, 1972 J- o. G L EET AL 3,687,660

DIFFUSION TRANSFER PHOTOGRAPHIC ELEMENTS COMPRISING 5HYDROXY-l-AZABENZIMIDAZOLE AND A SECOND AZABENZIMIDAZOLE, AND PROCESSES FORTHEIR USE Filed 0st. 15, 1970 2 Sheets-Sheet 2 .J l .Q N I l I N I 1' IN I w. l N 1 I m. I N I I r N co 0Q N, O (\i N 3 O O O O AllSNBCINouoauaa INVENTORS JAMES D GONDOLFE RUTH S CANLA'N JEANNE A.WARD' 3- WWATTORNEYS United States Patent U.S. Cl. 96-3 36 Claims ABSTRACT OF THEDISCLOSURE A novel combination of azebenzimidazoles is used for theprevention of fog formation in diffusion transfer photographicprocesses, which combination results in a dynamic range extension of thephotographic system.

The present invention relates to photography and more particularly tophotographic products and processes.

It has been extensively reported in literature pertaining to photographythat photosensitive silver halide emulsions, and particularlyphotosensitive gelatino-silver halide emulsions, have a tendency to losesensitivity and to become spontaneously developable without exposure tolight. This phenomenon, characterized as chemical fog, may be defined asthe density above base level that is developed in emulsion areas thathave received no intentional exposure and, in general, is not uniformlydistributed over a selectively photoexposed emulsion, being greatest inthe unexposed areas and decreasing with increased exposure in anon-linear manner.

In both silver and color photographic systems, the latter where silverhalides are used to control image dye formation, fog results in a lossof image acuity.

Chemical fog may be divided into two classes: inherent fog, that is, fogwhich is emulsion initiated; and induced fog, that is, fog which isinitiated during development. Induced fog appears to be due to physicaldevelopment about extra-granular centers and inherent fog is probablydue to the presence of grains bearing a catalytic site sensitivity speckwhich is unavoidably introduced and which is equivalent in itsproperties to latent image. Induced fog accordingly may be unaffected bythe level of inherent fog. Thus it will be readily appreciated that anemulsion susceptible to the development of chemical fog requires silverhalide grains possesing a catalytic center of sufficient size to bespontaneously developable and/or grains unprotected fromnon-discriminatory development.

Various and sundry procedures and additives have been disclosed in theart to provide an increase in the stability of photosensitive silverhalide emulsions by reducing the tendency of photosensitive compositionsto fog. These procedures usually increase the speed-to-fog ratio;otherwise there would be no point in using them unless the requirementfor a low fog level completely overrides that for sensitivity. Ingeneral, the methods available for the control of fog are to increasethe bromide ion concentration during the emulsion fabrication process;select fog free gelatins, i.e., gelatins which are free of foggingcontaminants and which have desirable ratios of restrainer tosensitizer; reduce the level of chemical sensitization; and addinorganic or organic fog retarding adjuncts.

This invention relates primarily to the latter item above, and moreparticularly to the use of a specified combination of synthetic, organicantifoggants.

Accordingly, it is a primary object of the present inmention to providenovel photographic products, and processes utilizing same, which exhibitdecreased suscepti- Patented Aug. 29, 1972 bility to fog formation, andat the same time, exhibit an extended exposure latitude.

Another object of the present invention is to provide novel processesand products, particularly adapted for obtaining monochromatic andmultichromatic images by diffusion transfer, which exhibit decreased fogformation throughout an extended temperature range, and at the sametime, exhibit an extended exposure latitude.

A still further object of the present invention is to provide novelphotographic elements comprising not less than one silver halideemulsion having associated therewith specified transfer image-formingcomponents which exhibit increased effective exposure latitude.

Other objects of the instant invention will in part be obvious and willin part appear hereinafter.

The invention accordingly comprises the process involving the severalsteps and the relation and order of one or more of such steps withrespect to each of the others and the product possessing the features,properties and the relation of the elements which are exemplified in thefollowing detailed disclosure and the scope of the application of whichwill be indicated in the claims.

For a fuller understanding of the nature and objects of the inventionreference should be had to the following detailed description taken inconnection with the accompanying drawings wherein:

FIG. 1 is a diagrammatic enlarged cross-sectional view of one embodimentof a film unit for obtaining multicolor images by a diffusion transferphotographic process illustrating the association of elements during onestage of the performance of a diffusion transfer process the thicknessof the various materials being exaggerated; and

FIG. 2 is a graph showing the characteristic curves of dye transferimages determined by plotting the reflection density of the transferimage, the red component thereof being taken as representative, as afunction of the log exposure of the photoresponsive silver halideemulsion, wherein Curve A (solid line) represents the charactertisticcurve of the red component of the transfer image prepared in accordancewith the present invention and employing the novel combination ofantifoggant materials as described herein, and Curve B (broken line)represents the charactertistic curve of the red component of thetransfer image prepared in accordance with heretofore known techniquesand employing an antifoggant component known to the prior art, saidcurves being set forth for the purpose of providing comparative data.

In diffusion transfer processes for the formation of transfer images, anexposed photographic emulsion is developed and, substantiallyconcurrently therewith, an imagewise distribution of transferimage-forming components is provided as a function of the point-to-pointdegree of development. At least part of that imagewise distribution istransferred by diffusion to a contiguous image-receiving layer toprovide the desired transfer image formation to that layer.

In diffusion transfer processes for the formation of silver transferimages, an exposed silver halide emulsion is developed and,substantially concurrently therewith, an imagewise distribution ofsoluble silver complex is obtained by reaction of a silver solvent withsilver halide of the emulsion as a function of its point-to-point degreeof exposure. Preferably, the photosensitive silver halide emulsion isdeveloped with a viscous processing composition which is spread betweenan element comprising the silver halide emulsion and a print receivingelement comprising a suitable silver precipitating layer. The processingcomposition affects development of the emulsion and substantiallycontemporaneously therewith forms a soluble silver complex, for example,a thiosulfate or thiocyanate, as a function of the point-to-point degreeof emulsion exposure. This soluble silver complex is, at least in part,transported in the direction of the print receiving element and thesilver thereof is largely precipitated in the silver precipitating layerof said element to form a transfer image therein.

U.S. Pats Nos. 2,647,049; 2,661,293; 2,698,244; 2,698,- 798; 2,802,735;3,148,062; 3,227,550; 3,227,551; 3,227,552; 3,227,554; 3,243,294;3,330,655; 3,347,- 671; 3,352,672; 3,364,022; 3,443,939; 3,443,940;3,443,- 941; 3,443,943; and 3,445,228 disclose subtractive colordiffusion transfer processes wherein color coupling techniques areutilized which comprise, at least in part, reacting one or moredeveloping agents and one or more color formers, as a function of thephotoexposure of a photo graphic emulsion, to provide a color image to asuperposed image-receiving layer. U.S. Pat. No. 3,019,124 discloses themanufacture of photographic color screen elements particularly adaptedfor employment in multicolor dilfusion transfer processes; and U.S.Pats. Nos. 2,968,554 and 2,983,606 disclose diffusion transfer processeswherein a color screen element is utilized to provide a multicolortransfer image to a superposed imagereceiving layer. U.S. Pats Nos.2,774,608; 2,983,606; 3,087,817; and 3,345,163 discloses diffusiontransfer processes wherein complete dyes are utilized to provide a colortransfer image to a superposed image-receiving layer.

As disclosed in the aforementioned U.S. Pat. No. 2,983,606, aphotosensitive element containing a dye developer and a silver halideemulsion is exposed and wetted by a liquid processing composition, forexample, by emersion, coating, spraying, flowing, etc., in the dark, andthe exposed photosensitive element is superposed prior to, during orafter wetting on a sheet-like support element which may be utilized asan image-receiving element. In a preferred embodiment, the liquidprocessing composition is applied to the photosensitive element in asubstantially uniform layer as the photosensitive element is broughtinto superposed relationship with the image-receiving layer. The liquidprocessing composition permeates the emulsion to initiate development.The dye developer is immobilized or precipitated in, for example,exposed areas as a function of the development. Such immobilization isapparently, at least in part, due to a change in the solubilitycharacteristics of the dye developer upon oxidation; particularly withregard to its solubility in alkaline solutions. It may also be due inpart to a tanning effect on the emulsion by oxidized developing agentand in part to a localized exhaustion of alkali as a result ofdevelopment. In the exposed and partially exposed areas of the emulsion,the dye developer, unreacted and diffusible, provides an imagewisedistribution of unoxidized dye developer dissolved in a liquidprocessing composition as a function of the point-to-point degree ofexposure of the silver halide emulsion. At least part of this imagewisedistribution of unoxidized dye developer is transferred by imbibition toa superposed image-receiving layer or element. Under certain conditionsthe layer of liquid processing composition may be utilized as theimage-receiving layer. The image-receiving element receives a depthwisediffusion of dye developer without appreciably disturbing the imagewisedistribution thereof to provide the color transfer image. Theimage-receiving element may contain agents adapted to mordant or other-Wise fix dye developer. If the color of the transferred dye developer isaifected by change in the pH of the image-receiving element, this pH maybe adjusted to provide a pH affording the desired color. The desired dyeimage carried by the image-receiving layer may be separated from thephotosensitive element by stripping at the end of a suitable imbibitionperiod.

In accordance with aforementioned U.S. Pat. No. 2,983,606, theimage-receiving layer need not be separated from its superposed contactwith the photosensitive element, subsequent to transfer image formation,if the image-receiving element is transparent and a processingcomposition containing a substance effective to mask the exposedphotosensitive element is spread between the image-receiving layer andthe silver halide emulsion layer.

Dye developers are compounds "which contain in the same molecule boththe chromophoric system of a dye and also a silver halide developingfunction. By a silver halide developing function is meant a groupingadapted to develop exposed silver halide. A preferred silver halidedeveloping function is a hydroquinonyl group. Other suitable developingfunctions include ortho-dihydroxyphenyl and orthoand para-aminosubstituted hydroxyphenyl groups. In general, the development functionincludes a benzenoid developing function, that is, an aromaticdeveloping group which forms quinonoid or quinone substances whenoxidized.

An extensive compilation of such compounds is set forth in theaforementioned U.S. Pat. No. 2,983,606 and, in particular, in thevarious U.S. patents and copending applications incorporated byreference therein.

In general, the preferred dye developers comprise monoazo andanthraquinone dyes which possess one or two hydroquinonyl groupsattached to the auxochromophobic system of the dye by means of aconjugationinterrupting divalent group such as, for example, an alkylenegroup.

Multicolored images may be obtained using color imageforming components,such as, for example, the previously mentioned dye developers, indiifusion transfer processes, by several techniques. One such techniquecon-templates the use of a photosensitive silver halide stratumcomprising at least two sets of selectively sensitized minutephotosensitive elements arranged in the form of a photosensitive screen.Transfer processes of this type are disclosed in the previously notedU.S. Patent No. 2,983,606. In such an embodiment each of the minutephotosensitive elements has associated therewith an appropriate dyedeveloper in or behind a silver halide emulsion portion. In general, asuitable photosensitive screen prepared in accordance 'with thedisclosure of said patent comprises minute red sensitized emulsionelements, minute green sensitized emulsion elements and minute bluesensitized emulsion elements arranged in side-by-side relationship in ascreen pattern and having associated therewith, respectively, a cyan dyedeveloper, a magenta dye developer and a yellow dye developer.

Another process for obtaining multicolor transfer images utilizing dyedevelopers employs an integral multilayer photosensitive element such asis disclosed in the aforementioned U.S. Patents Nos. 2,983,606 and3,345,- 163, wherein at least two selectively sensitized photosensitivestrata and associated dye developers are superposed on a single supportand are processed simultaneously and without separation with a singlecommon imagereceiving layer. A suitable arrangement of this typecomprises a support carrying a red-sensitive silver halide emulsionstratum, a green-sensitive silver halide emulsion stratum, and ablue-sensitive silver halide emulsion stratum, said emulsions havingassociated therewith respectively, for example, a cyan dye developer, amagenta dye developer and a yellow dye developer. The dye developer maybe utilized in the silver halide emulsion layer, for example, in theform of particles, or it may be employed as a layer behind theappropriate silver halide emulsion stratum, for example, a layer of dyedeveloper applied by the use of a coating solution containing about 0.5to 8%, by weight, of the respective dye developer. Each set of silverhalide emulsion and associated dye developer strata may be separatedfrom other sets by suitable interlayers, for example, gelatin and thesynthetic polymeric materials disclosed in copending application ofLloyd D. Taylor, Ser. No. 641,669, filed Feb. 7, 1967 (now U.S. PatentNo. 3,421,892 issued J an. 14, 1969). In certain instances it may bedesirable to incorporate a yellow filter in front of the green-sensitiveemulsion and such yellow filter may be incorporated in an interlayer.However, where desirable, a yellow dye developer of appropriate spectralcharacteristics which is present in a state capable of functioning as ayellow filter may be employed. In such instances a separate yellowfilter may be omitted.

The preceding color image-forming components, that is, dye developers,are preferably selected for their ability to provide colors that areuseful in carrying out subtractive color photography, i.e., cyan,magenta and yellow. It should be noted that it is within the scope ofthis invention to use mixtures of dye developers, for example, to obtaina desired color, e.g., black. Thus it is to be understood that theexpression color as used herein is intended to include the use of aplurality of colors to obtain black, as well as the use of a singleblack dye developer.

US. Patent No. 3,362,819, issued Jan. 1, 1968, discloses image-receivingelements, particularly adapted for employment in color diffusiontransfer processes, for example, of the type disclosed in aforementionedUS. Patent No. 2,983,606, which comprise a support layer possessing onone surface thereof, in sequence, a polymeric acid layer, an inerttiming layer or spacer layer in the preferred embodiment, and animage-receiving layer adapted to provide a visible image upon transferto said layer of diffusible dye image-forming substance.

As set forth in the last-mentioned application, the polymeric acid layercomprises polymers which contain acid groups, such as carboxylic acidand sulfonic acid groups, which are capable of forming salts with alkalimetals, such as sodium, potassium etc., or with organic bases,particuuarly quaternary ammonium bases, such as tetramethyl ammoniumhydroxide, or potentially acid-yielding groups, such as anhydrides orlactones, or other groups which are capable of reacting with bases tocapture and retain them. The acid-reacting group is, of course,nondiffusible from the acid polymer layer. In the preferred embodimentsdisclosed, the acid polymer contains free carboxyl groups and thetransfer processing composition employed contains a large concentrationof sodium and/or potassium ions. The acid polymers stated to be mostuseful are characterized by containing free carboxyl groups, beinginsouble in water in the free acid form, and by forming watersolublesodium and/or potassium salts. One may also employ polymers containingcarboxylic acid anhydride groups, at least some of which preferably havebeen converted to free carboxyl groups prior to imbibition. While themost readily available polymeric acids are derivatives of cellulose orof vinyl polymers, polymeric acids from other classes of polymers may beused.

The acid polymer layer is disclosed to contain at least sufficient acidgroups to effect a reduction in the pH of the image layer from a pH ofabout 12 to 14 to a pH of at least 11 or lower at the end of theim'bibition period, and preferably to a pH of about 5 to 8 Within ashort time after imbibition. The pH of the processing compositionemployed preferably is of the order of at least 12 to 14.

It is, of course, necessary that the action of the polymen'c acid be socontrolled as not to interfere with either development of the negativeor image transfer of unoxidized dye developers. For this reason, the pHof the image layer is kept at a level of pH 12 to 14 until the positivedye image has been formed after which the pH is reduced very rapidly toat least about pH 11, and preferably about pH 9 to 10, before thepositive transfer image is separated and exposed to air. Unoxidized dyedevelopers containing hydroquinonyl developing radicals diffuse from thenegative to the positive as the quaternary ammonium, sodium or otheralkali salt. The diffusion rate of such dye image-forming componentsthus is at least partly a function of the alkali concentration, and itis necessary that the pH of the image layer remain on the order of 12 to14 until transfer of the necessary quantity of dye has beenaccomplished. The subsequent pH reduction, in addition to its desirableeffect upon image light stability, serves a highly valuable photographicfunction by substantially terminating further dye transfer. Theprocessing technique thus effectively minimizes changes in color balanceas a result of longer imbibition times in multicolor, transfer processesusing multiplayer negatives.

Where the image-receiving element is maintained in contact with thephotosensitive element, subsequent to dye developer transfer imageformation, and includes the presence of an alkaline processingcomposition, necessarily having a pH at which dye developers, forexample, in reduced form, diffuse to form the dye transfer image,intermediate the elements, the transfer image thus formed is unstableover an extended period of time. The dye image instability is due, atleast in part to the presence of what is, in general, a relatively highpH alkaline composition in intimate contact with the dye or dyes formingthe image. This contact itself provides instability to the molecularstructure of dye by, for example, catalyzing degradation and undesirablestructural shifts effecting the spectral absorption characteristics ofthe image dye. In addition, the presence of an alkaline composition,possessing a pH at which the dye, for example, in reduced form, diffusesalso provides an integral dynamic system wherein oxidized dye,immobilized in areas of the photosensitive element, as a function of itsdevelopment, with the passage of time attempts to generate, in suchareas, an equilibrium between oxidized and reduced dye. In that the pHof the dynamic system is such that diffusion of the reduced form of thedye will occur, such reduced dye will, at least in part, transfer to theimage-receiving layer and the resultant diffusion will imbalance theequilibrium, in such areas of the photosensitive element, in favor ofadditional formation of reduced dye. As a function of the efliciency ofthe image-receiving layer, as a dye sink, such nonimage-wise dyeing ofthe image-carrying layer still further imbalances the equilibrium infavor of the additional formation of dye in reduced, dilfusible form.Under such circumstances, the transfer image definition, originallycarried by the image-receiving layer, will suffer a continuous decreasein the delta between the images maximum and minimum densities and may,ultimately, result in the image-receiving elements loss of all semblanceof image definition; merely becoming a polymeric stratum carrying arelatively uniform overall dyeing.

Any attempt to decrease the dye sink capacity of the image-carryinglayer, for example, by reduction of its mordant capacity, in order toalleviate, at least to an extent, the action of the image-receivinglayer as a dye sink, however, will enhance diffusion of the dye,comprising the transfer image, from the image-carrying layer, to theremainder of the element due, at least in part, to the continuedpresence of the alkaline composition having a pH at which the reducedform of the dye, forming the transfer image, is diffusible. The ultimateresult is substantially the same overall image distortion as occurs whenthe image-receiving layer acts as a dye sink, with the exception thatthe dye is more extensively distributed ,throughout the film unit andthe ultimate overall dyeing of the image-receiving layer itself is oflower saturation.

The problems inherent in fabricating a film unit of the type wherein theimage-receiving element, the alkaline processing composition and thephotosensitive element are maintained in contiguous contact subsequentto dye transfer image formation, for example, a film unit of the typedescribed hereinbefore with reference to aforementioned US. Pat. No.2,983,606, may be effectively obviated by fabrication of a film unit inaccordance with the physical parameters specifically set forth in US.Pat. Nos. 3,415,644; 3,415,645; and 3,415,646.

Specifically, an integral photographic film unit particularly adaptedfor the production of a dye transfer image of unexpectedly improvedstability and other properties, 'by a color diffusion transfer processwill be constructed, for example, in accordance with aforementioned US.Pat. No. 3,415,644, to include a photosensitive element com prising alaminate having, in sequence, as essential layers, a dimensionallystable opaque layer; a photosensitive silver halide emulsion layerhaving associated therewith dye image-providing material which issoluble and diifusible, in alkali, at a first pH; an alkaline solutionpermeable polymeric layer dyeable by the dye image-providing material; apolymeric acid layer such as those disclosed in aforementioned U.S. Pat.No. 3,362,819 containing sufficient acidifying groups to effectreduction, subsequent to substantial transfer dye image formation, of aselected processing solution having the first pH to a second pH at whichsaid dye image-providing material is insoluble and nondiffusible; and adimensionally stable transparent layer. In combination with thelaminate, a rupturable container retaining an aqueous alkalineprocessing composition having the first pH and containing a material,preferably a reflecting agent, in a quantity sufficient to mask the dyeimage-providing material, is fixedly positioned and extends transverse aleading edge of the laminate whereby to effect unidirectional dischargeof the containers contents between the alkaline solution permeable anddyeable polymeric layer and the photosensitive silver halide emulsionlayer next adjacent thereto, upon application of compressive force tothe container.

It will also be recognized that the dimensionally stable polymericsupport layer next adjacent the photosensitive silver halide emulsionlayer or layers may be transparent, as disclosed in aforementioned U.S.Patent No. 3,415,646, and that in such instance, the masking agent maybe initially dispersed in the composite film unit intermediate thedyeable polymeric layer and the silver halide emulsion layer nextadjacent, as disclosed in aforementioned U.S. Pat. No. 3,415,645.

Employment of the last-mentioned film units, according to the describedcolor diffusion transfer photographic process, specifically provides forthe production of a highly stable color transfer image accomplished, atleast in part, by effectively obviating the previously discusseddisadvantages of the prior art products and processes, by in processadjustment of the environmental pH of the film unit from a pH at whichtransfer processing is operative to a pH at which dye transfer isinoperative subsequent to substantial transfer image formation by meansof the stated polymeric acid layer. The stable color transfer image isobtained irrespective of the fact that the film unit is maintained as anintegral laminate unit during exposure, processing, viewing, and storageof the unit, which transfer image exhibits the required maximum andminimum dye transfer image densities, dye saturation, hues anddefinition.

In order to prevent premature pH reduction during transfer processing,as evidenced, for example, by an undesired reduction in positive imagedensity, the acid groups of the stated polymeric acid component aredisclosed to be so distributed in the acid polymer layer that the rateof their availability to the alkali is controllable, e.g., as a functionof the rate of swelling of the polymer layer which rate in turn has adirect relationship to the diffusion rate of the hydroxyl ions. Thedesired distribution of the acid groups in the acid polymer layer may beeffected by mixing the acid polymer with a polymer free of acid groups,or lower in concentration of acid groups, and compatible therewith, orby using only the acid polymer but selecting one having a relativelylower proportion of acid groups. These embodiments are illustrated,respectively, in aforementioned U.S. Patent No. 3,362,819, by (a) amixture of cellulose acetate and cellulose acetate hydrogen phthalateand (b) a cellulose acetate hydrogen phthalate polymer having a muchlower percentage of phthalyl groups than the first-mentioned celluloseacetate hydrogen phthalate.

It is also disclosed that the layer containing the polymeric acid maycontain a water insoluble polymer, preferably a cellulose ester, whichacts to control or modulate the rate at which the alkali salt of thepolymer acid is formed. As examples of cellulose esters contemplated foruse, mention is made of cellulose acetate, cellulose acetate, butyrate,etc. The particular polymers and combinations of polymers employed inany given embodiment are, of course, selected so as to have adequate wetand dry strength and when necessary or desirable, suitable subcoats maybe employed to help the various polymeric layers adhere to each otherduring storage and use.

The inert spacer layer of the aforementioned patent, for example, alayer comprising polyvinyl alcohol or gelatin, acts to time" control thepH reduction by the polymeric acid layer. This timing is disclosed to bea function of the rate at which the alkali diffuses through the inertspacer layer. It was stated to have been found that the pH does not dropuntil the alkali has passed through the spacer layer, i.e., the pH isnot reduced to any significant extent by the mere diffusion into thespacer layer, but the pH drops quite rapidly once the alkali diffusesthrough the spacer layer into the acid polymer layer.

It has been disclosed in U.S. Patent No. 3,455,686, issued July 15,1969, that the diffusion rate of an alkali processing compositionthrough a permeable inert polymeric spacer layer increases withincreased processing temperature to the extent, for example, that atrelatively high transfer processing temperature, that is, transferprocessing temperatures above approximately F., a premature decrease inthe pH of the transfer processing composition occurs due, at least inpart, to the rapid diffusion of alkali from the dye transfer environmentand its subsequent neutralization upon contact with the polymeric acidlayer. This was disclosed to be especially true of alkali traversing aninert spacer layer prossessing optimum alkali-permeabilitycharacteristics within the temperature range of optimum transferprocessing. Conversely, at temperatures below the optimum transferprocessing range, for example, temperatures below approximately 40 F.,the last-mentioned inert spacer layer was found to provide an effectivediffusion barrier timewise preventing effective traverse of the inertspacer layer by alkali having temperature depressed diffusion rates.This barrier resulted in maintenance of the transfer processingenvironrnents high pH for such an extended time interval as tofacilitate formation of transfer image stain and its resultantdegradation of the positive transfer images color definition.

It Was further disclosed in the last-mentioned patent, that if the inertspacer layer of the print-receiving element is replaced by a spacerlayer which comprises permeable polymeric layer exhibiting permeabilityinversely dependent upon temperature, and specifically a polymericfilmforming material which exhibits decreasing permeability tosolubilized alkali derived cations such as alkali metal and quaternaryammonium ions under conditions of increasing temperature, that thepositive transfer image defects resultant from the aforementionedover-extended pH maintenance and/or premature pH reduction wereobviated.

As examples of polymers disclosed in the last-mentioned patent whichexhibit inverse temperature-dependent permeability to alkali, mentionwas made of: hydroxypropyl polyvinyl alcohol, polyvinyl methyl ether,polyethylene oxide, polyvinyl oxazolidinone, hydroxypropyl methylcellulose, partial acetals of polyvinyl alcohol such as partialpolyvinyl butyral, partial polyvinyl formal, partial polyvinyl acetal,partial polyvinyl propional, and the like.

Additional polymers which may be particularly advantageously employedare temperature-inverting polyvinylamide graft copolymers, as disclosedin copending application Ser. No. 790,147, 'filed Jan. 13, 1969, in thename of Lloyd D. Taylor (new U.S. Patent No. 3,575,701 issued Apr. 20,1971).

Cope'nding application Ser. No. 782,075, filed Dec. 9, 1968 now PatentNo. 3,573,044 in the name of Edwin H. Land, discloses an alternativemeans for effectively obviating the problems inherent in fabricating afilm unit of the type where the image-receiving element, the alkaliprocessing composition and the photosensitive element are maintained incontiguous contact during processing and subsequent to dye transferimage formation, for example, a film unit of the type described, withreference to aforementioned U.S. Patent No. 2,983,606. Specifically, itis disclosed in US. Patent No. 3,573,044 that an integral photographicfilm unit of simplified construction and particularly adapted for theproduction of dye transfer images of improved stability and otherdesirable properties by a color diffusion transfer process can beconstructed to include a photosensitive element comprising a compositestructure possessing, in sequence, as essential layers, a firstdimensionally stable layer, a photosensitive silver halide emulsionlayer having associated therewith a dyeimage-forming material which issoluble and diffusible at a first processing composition solventconcentration, a polymeric layer dyeable by the dye image-formingmaterial, and a second dimensionally stable layer transparent toincident actinic radiation, wherein the dimensionally stable layerstaken together, possess a processing composition solvent vaporpermeability sufficient to effect, subsequent to substantial dyetransfer image formation and preceding substantial dye transfer imagedegradation, osmotic transpiration of processing composition solvent ina quantity effective to decrease the first solvent concentration, atwhich the dye image-forming material is soluble and dilfusible, to asecond solvent concentration, at which the dye image-forming material issubstantially nondiffusible. In combination with the compositestructure, a rupturable container retaining a processing compositioncomprising the solvent is fixedly positioned and extends transverse aleading edge of the composite structure whereby to effect, uponapplication of compressive pressure, discharge of the processingcomposition intermediate the dyeable polymeric layer and thephotosensitive silver halide emulsion layer next adjacent, in a quantitysufficient to provide the first solvent concentration.

Employment of the detailed film unit of the invention of thelast-mentioned copending application in color diffusion transferprocesses specifically provides for the production of a highly stabletransfer image accomplished, at least in part, by in process adjustmentof the environmental processing composition solvent concentration from asolvent concentration at which dye diffusion or transfer is operative toa solvent concentration at which dye transfer is inoperative subsequentto substantial transfer image formation.

Copending applications Ser. No. 867,626, filed Oct. 20, 1969, in thename of Terry W. Milligan (now US. Patent No. 3,597,197 issued Aug. 3,1971), and Ser. No. 867,583, filed Oct. 20, 1969, in the names ofSheldon A. Buckler, Terry W. Milligan, and Howard G. Rogers, now abandoned, disclose still other means for effectively obviating the problemsinherent in fabricating a film unit of the type where theimage-receiving element, the alkali processing composition and thephotosensitive element are maintained in contiguous contact duringprocessing and subsequent to dye transfer image formation.

Specifically, it is disclosed in aforementioned Ser. Nos. 867,626 and867,583 that an integral photographic film unit particularly adapted forthe production of dye transfer images of improved stability and otherdesirable properties by a color diffusion transfer process can be con?structed to include a photosensitive element comprising a compositestructure possessing, in sequence as essential layers, a firstdimensionally stable layer, a photosensitive silver halide emulsionlayer having associated therewith a dye image-forming material which issoluble and diffusible as a function of the point-to-point degree ofemulsion photoexposure, a polymeric layer dyeable by the dyeimage-forming material, and a second dimensionally stable layertransparent to incident actinic radiation. In

combination'with the composite structure, a rupturable containerretaining a processing composition is fixedly positioned and extendstransverse a leading edge of the composite structure whereby to effect,upon application of compressive pressure, discharge of the processingcomposition intermediate the dyeable polymeric layer and thephotosensitive silver halide emulsion and associated dye image-formingmaterial next adjacent thereto. In addition, the aforementioned integralphotographic film unit possesses means for interposing between saiddyeable polymeric layer and the photosensitive silver emulsion nextadjacent thereto, a continuous dye image forming material impermeablepolymeric layer after substantial image formation has been accomplishedin said dyeable polymeric layer in order to obviate further dyemigration. Means for the formation of such a continuous polymeric layerinclude, for example, incorporating in the processing composition aparticulate dispersion of a processing composition insoluble polymer asa discontinuous phase, said polymer being adapted, upon decrease inprocessing composition solvent, to coalesce at ambient temperature. Asexamples of processing composition insoluble polymers suitable for suchan application, mention may be made of the various polymeric solid andliquid materials which provide a latex when dispersed in a solvent inwhich they are insoluble and stable and, particularly when dispersed inwater possessing a preselected pH, known in the art to coalesce atambient temperatures and at relatively rapid rates upon loss ofdispersant solvent to provide relatively impermeable substantiallycontinuous films or polymeric layers including butadiene/ styrenecopolymers; polyacrylamides; polymethylmethacrylates; polyvinylchlorides and copolymers thereof; polyvinyl acetates and copolymersthereof; acrylonitrile/ethyl acrylate copolymers;acrylonitrile/styrene/butadiene terpolymers; and the like.

Other techniques for the formation of a continuous dye image-formingmaterial impermeable polymeric stratum, as disclosed in thelast-mentioned copending applications, include the coating of apolymeric material intermediate the polymeric dye image-receiving layerand the photosensitive silver halide emulsion layer next adjacentthereto with a polymeric material whose dye image-forming materialpermeability is a direct function of the pH of the system; i.e., as thepH of the system is increased the permeability of the polymeric layerincreases whereby dye image-forming material freely passes therethrough.However, as the pH of the system is decreased, e.g., by the use of apolymeric acid component of the type set forth in US. Pat. No.3,362,819, the permeability of such a material decreases to an ultimatepoint at which dye imageforming material is incapable of passingtherethrough. Such a system may be visualized as a pH valve. As examplesof polymeric materials which may be used to provide a substantiallycontinuous dye image-forming material impermeable stratum between theimage-receiving layer and the photosensitive silver halide emulsionlayer next adjacent thereto, mention may be made of the variouspolymeric materials which are known to act as a pH valve as aforenoted,such as, for example, polyphenolic polymers such as the acetal ofhydroxybenzaldehyde and polyvinyl alcohol; sulfonamides, such as, forexample, the acetal of a primary formyl benzene sulfonamide andpolyvinyl alcohol; polymers comprising a-trifluoromethylvinyl alcoholsegments; the benzene s'ulfonamide of deacetylated chitin;polyhydroxymethylene; the acetal of 3-hydroxybenzaldehyde and a vinylalcohol-atrifiuoromethylvinyl alcohol copolymer; novolactic phe nolformaldehyde polymers; Santolite MHP (trade name of Monsanto ChemicalCompany for a formaldehyde benzenesulfonamide condensation polymer);poly-m,a-bis(hydroxyethyl) methylene; etc. Generally speaking, suchmaterials comprise weakly ionized polymeric acids, for example, thosehaving an ionization constant between about 10- and 10 The above-denotedpolymeric compositions whose permeability is directly related to theenvironmental pH may be utilized by being dissolved in the alkalineprocessing composition and being spread between the image-receivinglayer and the next adjacent photosensitive layer to provide asubstantially continuous stratum; or such materials may be coatedintermediate the photosensitive silver halide emulsion next adjacent theimage-receiving layer, and the image-receiving layer, as a continuousfilm to be rendered permeable at such time as the processing compositioncontainer is ruptured to thereby release the alkaline processingcomposition whereby the pH valve is rendered permeable toimage-producing material until such time as the pH of the system isdropped below a dataum level.

In another system which is disclosed in copending application Ser. No.867,583 referred to supra, the viscosityincreasing ingredients utilizedin the processing composi tion are cross-linked subsequent tosubstantial image formation in the image-receiving layer to the extentrequired to provide an image-forming material impermeable layer betweenthe image-receiving layer and the next adjacent silver halide emulsionlayer. Such a system may be carried out by incorporating a ditfusiblecross-linking agent or suitable precursors thereof in the compositephotosensitive structure, which, following rupture of the processingcomposition container, diffuse into distributed processing compositionto thereby cross-link a thickening substance or other polymeric materialincorporated in said processing composition. As was discussed above,hydroxyethyl cellulose is commonly utilized as a viscosity-increasingagent in conventional diffusion transfer processes, as more fullydisclosed and discussed in numerous of the aforementioned patents andparticularly in US. Pat. No. 2,983,606; suitable cross-linking agentsfor this and similar materials include divinyl s-ulfone and precursorsthereof, e.g., bis-pyridinium ethyl sulfone chloride, and fl-ketoethylonium salts as disclosed in Us. Pat. No. 3,345,177.

A still further technique for accomplishing the abovedenoted barrierformation as disclosed in copending application Ser. No. 867,583 is toprovide a coating intermediate the dye image-forming layer and thephotosensitive silver halide emulsion next adjacent thereto wherein across-linking agent for the material comprising said coating isincorporated in an element of the photographic film unit whereby aftersubstantial image formation in the polymeric dye image-receiving layersufiicient cross-linking agent contacts said coating to render itsubstantially impermeable to dye image-forming materials. Thus, forexample, a polyvinyl alcohol overcoat may be utilized either over theimage-receiving layer or over the next adjacent photosensitive silverhalide layer, and a cross-linking agent therefor which will not have asubstantial deleterious etfect on gelatin may be incorporated within oneof the layers comprising the film unit, as, for example, in the denotedinterlayer between the red-sensitive silver halide emulsion layer andthe magenta dye developer layer. Within such an embodiment, for example,a boric acid cross-linking agent for polyvinyl alcohol may beincorporated in the above-denoted interlayer. Upon rupture of theprocessing composition container, processing composition is distributedbetween the image-receiving element and the negative element, renderingthe boric acid material diifusible within the system. As this materialcomes into contact with the polyvinyl alcohol overcoat between theimage-receiving layer and the next adjacent photosensitive emulsionlayer, the polyvinyl alcohol is cross-linked and becomes impermeable toimage-forming materials.

As examples of materials which heretofore have been found to be usefulas image-receiving layers in diifusion transfer color photographicprocesses, mention may be made of solution dyeable polymers such asnylons as, for example, N methoxymethyl polyhexamethylene adipa- 12mide; partially hydrolyzed polyvinyl acetate; polyvinyl alcohol with orWithout plasticizers; cellulose acetate with ifillers as, for example,one-half cellulose acetate and onehalf oleic acid; gelatin; and othermaterials of a similar nature. Particularly useful materials havecomprised polyvinyl alcohol or gelatin, having admixed therewith a dyemordant such as poly-4-vinylpyridine, as disclosed in US. Pat. No.3,148,061, issued Sept. 8, 1964, or vinylpyridine graft copolymers asdisclosed in copending application Ser. No. 58,685 filed July 27, 1970,in the name of Stanley P. Bedell (now abandoned and replaced by acontinuationin-part application, Ser. No. 156,035 filed June 23, 1971).

As disclosed in the previously cited patent, the liquid processingcomposition referred to for effecting monochromatic and multicolortransfer processes comprises at least an aqueous solution of an alkalinecompound, for example, diethylamine, sodium hydroxide or sodiumcarbonate and possesses a pH in excess of 12 preferably. If the liquidprocessing composition is to be applied to the emulsion by being spreadthereon, preferably in a relatively thin uniform layer, it includes aviscosity-increasing compound consituting a film-forming material of thetype which, when said composition is spread and dried, forms arelatively firm and relatively stable film. A preferred filmformingmaterial is a high molecular weight polymer such as a polymeric,water-soluble ether which is inert to an alkaline solution such as, forexample, a hydroxyethyl cellulose or sodium carboxymethyl cellulose.Other filmforming materials or thickening agents whose ability toincrease viscosity is substantially unaffected if left in solution for along period of time may also be used. The filmforming material ispreferably contained in the processing composition in suitablequantities to impart to said composition a viscosity in excess of 1,000centipoises at a temperature of approximately 24 C. and preferably ofthe order of 1,000 to 200,000 centipoises at said temperature.Illustrations of suitable liquid processing compositions may be found inthe several patents and copending applications herein mentioned and alsoin examples herein given. Under certain circumstances, it may bedesirable to apply a liquid processing composition to the photosensitiveelement prior to exposure, in accordance with the technique described inUS. Pat. No. 3,087,816, issued Apr. 30, 1963.

It will be noted that the liquid processing composition employed maycontain an auxiliary or accelerating developing agent, such asp-methylaminophenol, 2,4-diaminophenol, p-benzylaminophenol,hydroquinone, toluhydroquinone, phenylhydroquinone,4'-methylpl1enylhydroquinone, etc. It is also contemplated to employ aplurality of auxiliary or accelerating developing agents, such as a3-pyrazolidone developing agent and a benzenoid developing agent, asdisclosed in US. Pat. No. 3,039,869, issued June 19, 1962. As examplesof suitable combinations of auxiliary developing agents, mention may bemade of 1-phenyl-3-pyrazolidone in combination with p-benzylaminophenoland 1-phenyl-3-pyrazolidone in combination with2,5-bis-ethyleneimino-hydroquinone. Such auxiliary developing agents maybe employed in the liquid processing composition or they may beinitially incorporated, at least in part, in one or more permeablestrata of the film unit. It may be noted that at least a portion of thedye developer oxidized during development may be oxidized andimmobilized as a result of a reaction, e.g., an energytransfer reaction,with the oxidation product of an oxidized auxiliary developing agent,the latter developing agent being oxidized by the development of exposedsilver halide. Such a reaction of oxidized developing agent withunoxidized dye developer would regenerate the auxiliary developing agentfor further reaction with the exposed silver halide.

In addition, development may be desirably effected in the presence of anonium compound, particularly a quaternary ammonium compound, inaccordance with the processes disclosed in US. Pat. No. 3,173,786. Also,color image quality may be enhanced by effecting development in thepresence of imidazole, as disclosed in US. Pat. No. 3,377,166.

As has been alluded to above, the presence of an antifoggant in aphotographic system may be responsible for reducing both inherent andinduced fog and will, therefore, produce a more attractive end product,both from aesthetic and technological points of view. Such productsdoubtless have a competitive advantage over other photographic productsnot quite as attractive or technologically efficient. The antifoggantcomposition is particularly helpful in minimizing or preventing reactionof a dye developer with unexposed silver halide and may be added to theprocessing composition and/or to one or more processing compositionpermeable layers of the photosensitive and/ or image-receiving elements.The pertinent art has recognized many compounds which have foginhibiting characteristics, such as sodium and potassium bromide andiodide, 6-nitro-benzimidazole, benzotriazole, chlorobenzotriazole,S-methyl-benzimidazole, 2-amino-benzimidazole, thio acetanilide, etc.

At low temperatures, when processing composition is distributed upon thecontact surface of a selectively exposed photosensitive element, of theaforementioned tripack configuration, development begins first in thebluesensitive emulsion, since it contacts the processing compositionbefore the other layers. Temperature-retarded development, however, isslowed up even more by the restraining properties of antifoggant presentand results, for example, in increased uncontrolled yellow dye developer transfer from the blue-sensitive emulsion to the image-receivinglayer before complete developmental control has been established. Thiscauses what may be termed yellow stain. It will be evident that at hightemperatures the precise opposite happens, that is, the development rateis accelerated to a point where the restraining effect of theantifoggant is of insufiicient consequence. The blue-sensitive emulsionwill then be developed and the properly developed silver, combined withthe fog present, will cause an over-control and thereby hold back thedesired image wise yellow dye diffusion and result in an undesired shiftin color balance of the transfer image.

U.S. Bat. 3,473,924, issued Oct. 21, 1969, discloses that a certainclass of azabenzimidazoles act as excellent antifoggants particularlyadapted for advantageous employment in diffusion transfer photographicprocesses to provide improved latitude in the temperatures at which suchprocess may be carried out. It was also disclosed therein that, inaddition to their unique antifogging characteristics, the designatedazabenzimidazoles may be incorporated into photographic systems withsubstantially no sacrifice of the effective speed of the transferprocess.

The last-mentioned patent teaches that the designated azabenzimidazoleantifoggants may be used alone or in conjunction with other conventionalantifoggants. F or eX- ample, with respect to a typical color filmprocessing composition containing a conventional antifoggant such asbenzotriazole and the like, generally in the order to about 2%, it wasdisclosed that the designated azabenzimidazole could be added to thesystem with a concomitant reduction in the percentage of or eliminationof the benzotriazole. In preferred embodiments, the azabenzimidazoleantifoggants were utilized in conjunction with a conventionalantifoggant compound, such as benzotriazole, whose effectivenessresponds normally to changes in temperature, to provide to the systemdevelopment and control characteristics satisfactory over a greatertemperature range than that achieved by the teachings set forth in theart. There was, however, no suggestion that any combination of two ormore of the designated azabenzimidazole antifoggants might be employedin the systems described, or that any particular advantage might begained thereby.

It has now unexpectedly been discovered that certain combinations ofazabenzimidazole compounds when employed as antifoggants in diffusiontransfer photographic processes provide not only improved temperaturelatitude without sacrifice of effective speed, but also, improvedexposure latitude in the photographic system. Specifically, it has nowbeen found that the use of antifoggant comprising a firstazabenzimidazole consisting of 5-hydroxy-4-azabenzimidazole incombination with a second azabenzimidazole of the formula:

where R is selected from the group consisting of hydrogen and loweralkyl groups, i.e., containing less than six carbon atoms; and R and Rare each selected from the group consisting of hydrogen, halogen, loweralkyl, i.e., containing less than six carbon atoms, nitro, lower alkoxyi.e., containing less than six carbon atoms, aryl, sulfonamido, andcarboxamido groups, it being understood that R and R taken together mayform an annulated hydrocarbon ring system, in diffusion transferphotographic processes of the type described, results in a widerexposure range over which useful information may be effectively recordedin the processed positive print.

Illustrative of the compounds which may be utilized as the secondazabenzimidazole component in the present invention are:

r o1 N 01- C (I) (IN/ N HaCA@\N} i ii crnson'v- \N t O N Brme /E v In apreferred embodiment of the present invention, a photosensitive elementis employed which is specifically adapted to provide for the productionof a multicolor dye transfer image and comprises a dimensionally stablesupport layer carrying at least two selectively sensitized silver halideemulsion strata each having a dye developer material of predeterminedcolor associated therewith which is soluble and diffusible in alkali ata first pH.

The preferred photosensitive image-receiving element comprises analkaline solution permeable polymeric layer dyeable by the dyedeveloper; a polymeric spacer layer comprising a polymer possessingdecreasing alkaline solution permeability with increasing temperature;an alkaline solution permeable polymeric acid layer containingsufiicient acidifying groups to effect reduction, subsequent tosubstantial multicolor transfer dye image formation, of theimage-receiving element from the first pH- to a second pH, at which thedye image-providing material is insoluble and nondiffusible; and adimensionally stable support layer.

The silver halide emulsions comprising the multicolor photosensitivelaminate preferably possess predominant spectral sensitivity to separateregions of the spectrum and each has associated therewith a dye, whichis a silver halide developing agent and is, most preferably,substantially soluble in the reduced form only at the first pH,possessing a spectral absorption range substantially complementary tothe predominant sensitivity range of its associated emulsion. In thepreferred embodiment, each of the emulsion strata, and its associateddye, is separated from the remaining emulsion strata, and theirassociated dye, by separate alkaline solution permeable polymericinterlayers.

In such preferred embodiment of the invention, the silver halideemulsion comprises photosensitive silver halide dispersed in gelatin andis about 0.6 to 6 microns in thickness; the dye itself is dispersed inan aqueous alkaline solution polymeric binder, preferably gelatin, as aseparate layer about 1 to 7 microns in thickness; the alkaline solutionpermeable polymeric interlayers are about 1 to 5 microns in thickness;the alkaline solution permeable and dyeable polymeric layer istransparent and about 0.25 to 0.4 mil in thickness; the polymeric spacerlayer intermediate the dyeable polymeric layer and the polymeric acidlayer is transparent and about 0.1 to 0.7 mil in thickness; the alkalinesolution permeable polymeric acid layer is transparent and about 0.3 to1.5 mils in thickness; and each of the dimensionally stable supportlayers are alkaline solution impermeable and about 2 to 6 mils inthickness. It will be specifically recognized that the relativedimensions recited above may be appropriately modified, in accordancewith the desires of the operator, with respect to the specific productto be ultimately prepared.

In the preferred embodiment of the present inventions film unit for theproduction of a multicolor transfer image, the respective silverhalide/dye developer units of the photosensitive element will be in theform of a tripack configuration which will ordinarily comprise a cyandye developer/red-sensitive emulsion unit contiguous the dimensionallystable support layer, the yellow dye developer/blue-sensitive emulsionunit most distant from the support layer and the magenta dye developer/green-sensitive emulsion unit intermediate those units, recognizing thatthe relative order of such units may be varied in accordance with thedesires of the operator.

Reference is now made to FIG. 1 of the drawing wherein there isillustrated a preferred film unit of the present invention.

As illustrated in FIG. 1, film unit 10 comprises a photosensitivelaminate 11 including, in order, dimensionally stable support layer 12,preferably a flexible sheet material; cyan dye developer layer 13;red-sensitive silver halide emulsion layer 14; interlayer 15, magentadye developer layer 16; green-sensitive silver halide emulsion layer 17;interlayer 18; yellow dye developer layer 19; blue-sensitive silverhalide emulsion layer 20; auxiliary layer 21, which may contain anauxiliary silver halide developing agent; and an image-receiving element22 including image-receiving layer 23; spacer layer 24; neutralizinglayer 25; and dimensionally stable support layer 26, preferably aflexible sheet material.

As shown in the drawing, the multilayer exposed photosensitive element11 is shown in processing relationship with an image-receiving element22 and a layer 27 of processing solution distributed intermediateelements 11 and 22.

In the performance of a diffusion transfer multicolor process employingfilm unit 10, the unit is exposed to radiation, actinic tophotosensitive laminate 11.

Subsequent to exposure, film unit 10 may be processed by being passedthrough opposed suitably gapped rolls in order to apply compressivepressure to a frangible container in order and to effect rupture of thecontainer and distribution of alkaline processing composition 27, havinga pH at which the cyan, magenta and yellow dye developers are solubleand difiusible, intermediate dyeable polymeric layer 23 and auxiliarylayer 21.

Alkaline processing solution 27 permeates emulsion layers 14, 17 and 20to initiate development of the latent images contained in the respectiveemulsions. The cyan, magenta and yellow dye developers, of layers 13, 16and 19, are immobilized, as a function of the development of theirrespective associated silver halide emulsions, preferably substantiallyas a result of their conversion from the reduced form to theirrelatively insoluble and nondiffusible oxidized form, thereby providingimagewise distributions of mobile, soluble and diffusible cyan, magentaand yellow dye developer, as a function of the point-to-point degree oftheir associated emulsions exposure. At least part of the imagewisedistributions of mobile cyan, magenta and yellow dye developertransfers, by diffusion, to aqueous alkaline solution permeablepolymeric layer 23 to provide a multicolor dye transfer image to thatlayer. Subsequent to substantial transfer image formation, a suflicientportion of the ions comprising aqueous alkaline solution 27 transfers,by diffusion, through permeable polymeric layer 23, permeable spacerlayer 24 and to permeable polymeric acid layer 25 Whereby alkalinesolution 27 decreases in pH, as a function of neutralization, to a pH atwhich the cyan, magenta and yellow dye developers, in the reduced form,are insoluble and nondiffusible, to provide thereby a stable multicolordye transfer image.

Subsequent to substantial transfer image formation, print-receivingelement 22 may be manually dissociated from the remainder of the filmunit, for example, by stripping.

Alternatively, where support layer 26 is transparent and alkalineprocessing composition 27 includes a reflect ing material capable ofmasking photosensitive element 11, print-receiving element 22 need notbe dissociated from the remainder of the film unit, but may bemaintained in superposed relationship thereto; the final positive imageis then viewable through transparent support layer 26.

As examples of reflecting materials, mention may be made of bariumsulfate, zinc oxide, titanium dioxide, barium stearate, silver flake,silicates, alumina, zirconium oxide, zirconium acetyl acetate, sodiumzirconium sulfate, kaolin, mica, and the like.

A particularly preferred agent comprises titanium di oxide due to itshighly effective reflection properties. In general, based upon percenttitanium dioxide (weight volume), a processing composition containingabout 40- 70 grams of titanium dioxide dispersed in 100 cc. of waterWill provide a percent reflectance of about -90% In the most preferredembodiments, the percent reflectance particularly desired will be in theorder of above 85%.

The present invention will be illustrated in greater detail inconjunction with the specific examples which will follow, which set outrepresentative photographic products and processes but which, however,are also intended to be illustrative and not of limiting effect. Theexamples will clearly show the extended exposure range over which usefulinformation may be elfectively recorded in the positive print whenprocessing is carried out in the presence of the novel azabenzimidazolecombination of the present invention, as evidenced by an extendedDynamic Range and overall improvement in the shape 17 of thecharacteristic curve, described herein after, of the transfer image.

The American Standards Association, Incorporated, has establishedstandards for quantitative evaluation of the sensitivity ofphotosensitive materials. These standards specify techniques forplot-ting the characteristic H and D curve of a negative material, thatis, the curve relating to the logarithm of the original exposure of thenegative to density in said negative. These techniques are described indetail in the publication of the American Standards Association,Incorporated, PH 2.5-1954, and titled American Standard Method forDetermining Photographic Speed and Exposure Index. In diffusion transferprocesses, a similar evaluation of reflection prints may be based on acurve relating original exposure of the negative to the density in theresultant positive, i.e., a curve plotting the reflecting density of thepositive as a function of the log exposure of the negative.

As will be recognized, and as employed herein in the examples which willfollow, the Dynamic Range of a diffusion transfer image comprises anempirically derived relative measurement of the range of exposure fromwhich a useful transfer image may be derived. This range is determinedby subtracting the log exposure value determined at the point on the toeportion of the transfer images characteristic curve where the gradientis 0.4from the log exposure value determined at the point on theshoulder portion of the curve, where the gradient is 0.4. The resultantgradient range is then equivalent to the log of the ratio of the 0.4 toegradient to the 0.4 shoulder gradient in units of exposure. The anti-logof the resultant exposure gradient provides the ratio of minimum tomaximum exposure in a subject which can be usefully recorded by the filmand is designated as the Dynamic Range.

The speed of the photosensitive material comprises generally anempirically derived relative measurement which may be defined as a valuerepresenting the reciprocal of the exposure required to produce a givenresult. Any precise valuation of speed," therefore, is based upon theselection of a particular reference point on the density scale of thecharacteristic curve for the material. Thus, for diffusion transfersystems wherein the-characteristic curve relates to the positivetransfer image, as used in the examples which will follow, shoulderspeed is the minimum amount of exposure which can be used to expose thenegative emulsion and give a transfer image in which there is theminimum contrast which the eye can distinguish, i.e., there is visibledetail in the shadow regions of the transfer image. This exposure isdetermined at the point on the shoulder portion of the previouslydescribed characteristic curve of the positive transfer image where thegradient is 0.4. Similarly, in the examples which will follow, 0.6 speedrefers to the amount of exposure needed to result in a positive transferimage having a density of 0.6 on the density scale of the characteristiccurve.

The toe of the characteristic curve of a positive transfer image refersto the point in the curve where the system begins to respond to reduceexposure from high intensity to lower intensities. The toe extent, then,as used in the examples which will follow, refers to that portion of thecharacteristic curve of a positive transfer image wherein the eye canbegin to distinguish" density differences in the image at high intensityexposures, and may be determined by the horizontal distance between thepoint on the toe portion of the curve where the gradient is 1.0 and thepoint on the toe portion of the curve where the gradient is 0.2.

The slope of designated central portions of the characteristic curve ofa position transfer image may be used as an indication of the tonalrange of these portions of the system; thus, a low slope value isindicative of a film having the ability to record a large range oftones, whereas a higher slope value reflects'a correspondingly smallerrange of tones. In the examples which will follow, two

difierent measurements of slope are reported: A- A1 slope and -40normalized slope. The A% slope may be determined by the formula:

where Y is the point on the density scale of the characteristic curvecorresponding to D max. min.)

Y is the point on the density scale corresponding to D (D D X is theexposure needed to result in the density represented by the value Y andX is the exposure resulting in the density represented by the value Y(It will be understood, of course, that D and D refer respectively tothe highest and lowest optical density points in the characteristiccurve.) The 9040 normalized slope is a similar measurement, but whichenables a more direct comparison of the tonal ranges of positive colorimages having different color saturations and densities; it may bedetermined by the formula D max. unn.

where S9040 is the slope of the curve between the .9 and .4 densityintercepts.

EXAMPLE 1 An image-receiving element was prepared by coating atransparent polyethylene terephthalate base with the partial butyl esterof polyethylene/maleic anhydride copolymer prepared by refluxing, for 14hours, 300 g. of a DX-84031 resin (trade name of Monsanto Chemical Co.,St. Louis, Mo., for high viscosity polyethylene/maleic anhydride), g. ofn-butyl alcohol and 1 cc. of 85% phosphoric acid to provide a polymericacid layer approximately 0.7 mil thick. The external surface of saidacid layer was coated with an emulsion comprising a graft copolymer ofdiacetone acrylamide and acrylamide on polyvinyl alcohol at a coverageof 750 mg./ft. to provide a spacer layer. (Spacer layers for diffusiontransfer color image-receiving elements comprising graft vinylamidecopolymers and procedures for preparing such polymers are described incopending application Ser. No. 790,747, filed Jan. 13, 1969, in the nameof Lloyd D. Taylor.) The external surface of thespacer layer was thencoated with a 2:1 mixture, by weight, of polyvinyl alcohol and poly-4-vinylpyridine, at a coverage of approximately 600 mgs. per square foot,to provide a polymeric image-receiving layer approximately 0.40 milthick. The thus-prepared image-receiving element was then baked at F.for 30 minutes and then allowed to cool.

A multicolor, multilayer photosensitive element was prepared in a mannersimilar to that disclosed in the aforementioned U.S. Patent No.3,345,163 and detailed hereinbefore. In general, the photosensitiveelements comprised a support carrying a red-sensitive silver halideemulsion stratum, a green-sensitive silver halide emulsion stratum and ablue-sensitive silver halide emulsion stratum. In turn, the emulsionshad dispersed behind'them in water: immiscible organic solvents andcontained in separate gelatin polymeric layers, respectively, a cyan dyedeveloper, a magenta dye developer and a yellow dye developer. A vinylamide polymer interlayer was positioned between the yellow dye developerlayer and the greensensitive emulsion stratum, and also between themagenta dye developer layer and the red-sensitive emulsion stratum.(Interlayers for diffusion transfer color photosensitive elementscomprising vinyl amide polymers and procedures for preparing suchpolymers are described in U.S. Patent No. 3,575,700 issued Apr. 20, 1971on copending application Ser. No. 790,648, filed Jan. 13, 1969, in thename of Lloyd D. Taylor.) The particular? dye developers employed weremetal-complexed dye developers of the following formulae:

N=C /O-N 3E1 011 l \N/ SO:NH?H C c CH2 Ho l I NCuN OH 1 a I C l O HOHo-NH-ms /N\ t CH: N=C c I (3133 OH SO2NH-()H OH: HO

a cyan dye developer;

no-cm-cm N-SOz- N=N "-011, HO-CHz-CH: l N 1?/ \eo if 0 O-c-omama magentadye developer; and

' ot nfi. N02

/C;H2o if on fi-o-om-on I OH a yellow dye developer. Metallized dyedevelopers of the foregoing types are described in U.S. Pat. No.3,482,972, issued Dec. 9, 1969, and in copending applications Ser. No.851,525, filed June 30, 1969; Ser. No. 798,438, filed Feb. 11, 1969 nowU.S. Pat. 3,563,739; Ser. No. 804,315, filed Mar. 4, 1969 now U.S. Pat.3,597,200; and Ser. No. 830,499, filed June 4, 1969 now U.S. Pat.3,551,406, all in the name of Martin Idelson; and Ser. No. 830,480,filed June 4, 1969, in the names of Arthur B. Goulston and Paul S.Huyfier.

The photosensitive element was then exposed to an analytical target, andprocessed for three minutes at room temperature by spreading aprocessing composition comprising:

water-IOO cc. potassium hydroxide (85% aqueous solution)-ll.2 g. sodiumcarboxymethyl cellulose-3.4 g. titanium dioxide-50.0 g.

phenethyl-a-picolinium bromide-4.37 g. 5-hydroxy-4-azabenzimidazole-O.35g. 6-bromo-5-methyl-4-azabenzimidazole0.23 g.

between the photoexposed emulsion and the image-receiving element in athin layer approximately 0.0028 inch thick. The resulting positive imageexhibited the following characteristics:

Dynamic Shoulder Toe 0. 6 normalrange speed extent speed slope lzedslope Red 23 2. 14 4 1 1. 32 1. 48 79 Green 26 2. 10 51 1. 09 1. 10 64Blue 22 2. 0O 37 .97 80 70 EXAMPLE 2 The process of Example 1 wasrepeated, except that the processing composition included an additionalconven tional antifoggant component:

benzotriazole.1.73 g.

The resulting positive image showed a D of 2.21 (red), 2.15 (green), and1.93 (blue) and a D of .05 (red), .19 (green), and .24 (blue), andexhibited the following characteristics:

Dynamic Shoulder Tue 0. 6 normalrange speed extent speed slope izedslope Red 25 1.76 .32 .95 1. 98 .84

Green 44 2. 00 40 1. 46 67 Blue 42 2. 00 45 .79 1. 2A 68 EXAMPLE 3 Theprocess of Example 1 was repeated, except that the processingcomposition additionally included:

imidazole1.73 g. The resulting positive image showed a Dmax, of 2.12(red), 2.15 (green), and 1.88 (blue) and a D of .05 (red),

.22 (green), and .24 (blue), and exhibited the followingcharacteristics:

Dynamic Shoulder Toe 0. 6 normalrange speed extent speed slope izedslope Red 26 2. 14 34 1. 17 1. 81 83 Green 34 2. l8 44 1.03 1.62 61 Blue29 2. 10 44: 1. 00 1. 22 68 EXAMPLE 4 The process of Example 2 wasrepeated, except that 5 hydroxy 4 azabenzimidazole was omittedaltogether from the processing composition. The resulting positive imageexhibited the following characteristics:

90-4 Dynamic Shoulder Tee 0. 6 M% normalrange speed extent speed slopeized slope Red 15 1. 44 32 70 2. 45 1. 00 Green 18 1. 46 32 56 1. 80 75Blue 14 1. 32 47 1. 14 81 The toe extent for blue was essentiallynon-existent, owing to the slow blue speed in this example.

EXAMPLE 5 The process of Example 2 was repeated, except that 6 bromo 5methyl 4 azabenzi-midazole was omitted altogether from the processingcomposition, and 1.72 g. of phenethylpicolinium bromide per cc. of waterwas employed. The resulting positive image exhibited the followingcharacteristics:

The process of Example 3 was repeated, except that hydroxy 4azabenzimidazole was omitted altogether from the processing composition.The resulting positive image exhibited the following characteristics:

Dynamic Shoulder Toe 0. 6 M% normalrange speed extent speed slope izedslope Red 16 1. 77 30 92 2. 58 1. 02

Green 24 1. 80 25 68 1. 87 71 Blue 22 1. 75 29 65 l. 67 74 EXAMPLE 7 Theprocess of Example 3 was repeated, except that 6 bromo 5 methyl 4azabenzimidazole was omitted altogether from the processing composition.The resulting positive image exhibited a dynamic range of 13 (red), 15(green), and 13 (blue), and a 90-40 normalized slope of 1.07 (red), .76(green), and .87 (blue).

FIG. 2 shows characteristic curves of the red components of the transferimages prepared in Examples 3 and 6, wherein Curve A (solid line)represents the characteristic curve of the red component of the transferimage of Example 3, and Curve B (broken line) represents thecharacteristic curve of the red component of the transfer image ofExample 6. The difference in characteristic curve shapes provides aclear graphic representation of the type of increase in tonal rangewhich may be gained using the novel antifoggant combination of thepresent invention.

Experiments similar to that of Example 3 were conducted using6-methyl-4-azabenzimidazole in combination with5-hydroxy-4-azabenzimidazole. It was observed that the resultingtransfer images exhibited results similar to those obtained in Example3, particularly with respect to greater dynamic range, faster 0.6 speed,and lower stain as compared with control experiments not containing5-hydroxy-4 azabenzimidazole. Similar results were obtained inexperiments wherein the antifoggant component comprised a combination of6 chloro-4-azabenzimidazole and 5-hydroxy-4-azabenzimidazole.

The procedures for synthesizing all of the azabenzimidazole componentsof the present invention are detailed in U .8. Patent 3,473,924,referred to previously.

In general, the optimum concentration of the total antifoggant componentto be employed should be determined empirically for each specificphotographic system. In general, such concentration range is between0.005 to 5.0 mgs. per millimole of silver halide present in the silverhalide emulsion of concern, depending on the fogging characteristics ofthe silver halide emulsion. In a preferred embodiment, the incorporationof from between about 0.15 to 2.0 g. of the combination of compounds ofthe present invention per 100 cc. of the processing composition utilizedin the diifusion transfer photographic process, provides particularlydesirable results. Although con centrations in excess of the firstmentioned range may be employed, an increase in the concentration beyondthe designated limits generally provides no additional beneficialresults. Conversely, concentrations below that of the designated rangemerely decrease fog control below the effective levels generally sought,but do not negate the achievement of some beneficial fog control.

With regard to the relative concentrations of 5-hydroxy 4azabenzimidazole and the second azabenzimidazole component as detailedhereinbefore, it has been found that mole ratios ofS-hydroxy-4-azabenzimidazole to the second azabenzimidazole component offrom about 1:0.14 to about 1:20 provide the extended exposure latitudeas described in the foregoing examples.

The agents themselves may be initially disposed in any one or moreprocessing composition permeable layers of the film nnits photosensitiveand/or image-receiving elements, for example, at any stage during itsmanufacture, in supplementation of, or in replacement of, the previouslyillustrated disposition as a component of the processing composition.

The support layers referred to may comprise any of the various types ofconventional rigid or flexible supports, for example, glass, paper,metal, and polymeric films of both synthetic types and those derivedfrom naturally occurring products. Suitable materials include paper;polymethacrylic acid, methyl and ethylesters; vinyl chloride polymers;polyvinyl acetal; polyamides such as nylon; polyesters such as polymericfilms derived from ethylene glycol terephthalic acid and cellulosederivatives such as cellulose acetate, triacetate, nitrate, propionate,butyrate, acetate-propionate, or acetate-butyrate.

It will be understood that silver halides of varying halideconcentrations may be advantageously employed and that the silver halideemulsions employed may be sensitized chemically and optically by any ofthe accepted procedures.

While a rupturable container provides a convenient means for spreading aliquid processing composition between layers of a film unit whereby topermit the processing to be carried out within a camera apparatus, thepractices of this invention may be otherwise effected. For example, aphotosensitive element, after exposure in suitable apparatus and whilepreventing further exposure thereafter to actinic light, may be removedfrom such apparatus and permeated with the liquid processingcomposition, as by coating the composition on said photosensitiveelement or otherwise wetting said element with the composition,following which the permeated, exposed photosensitive element, still,without additional exposure to actinic light, is brought into contactwith the image-receiving element for image formation in the mannerheretofore described.

In all examples of this specification, percentages of components aregiven by weight unless otherwise indicated.

Throughout the specification and appended claims; the expressionpositive image has been used. This expression should not be interpretedin a restrictive sense since it is used primarily for purposes ofillustration, in that it defines the image produced on theimage-carrying layer as being reversed, in the positive-negative sense,with respect to the image in the photosensitive element. As an exampleof an alternative meaning for positive image, assume that thephotosensitive element is exposed to actinic light through a negativetransparency. In this case, the latent image in the photosensitiveelement will be a positive and the image produced on the image-carryinglayer will be a negative. The expression positive image is intended tocover such an image produced on the image-carrying layer.

Throughout the specification and claims, the expression superposing hasbeen used. This expression is intended to cover the arrangement of twolayers in overlying relation to each other either in face-to-facecontact or in separated condition and including between them at leastone layer or stratum of a material which may be a viscous liquid.

Since certain changes may be made in the above products, compositionsand processes without departing from the scope of the invention hereininvolved, it is intended that all matter contained in the abovedescription shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. In a process for forming a photographic silver image which comprisesthe step of developing an exposed photosensitive element containing asilver halide emulsion with an aqueous processing composition, theimprovement which comprises conducting said process in the presence ofan eifective amount of an antifoggant composition comprising thecombination of a first azabenzimidazole consisting ofS-hydroxy-4-azabenzimidazole and a second azabenzimidazole of theformula wherein R is hydrogen or a lower alkyl group; and R and R areeach hydrogen, halogen, lower al-kyl, nitro, lower alkoxy, aryl,sulfonamido, or carboxamido groups.

2. A process as defined in claim 1 wherein said second azabenzimidazoleis d-bromo 5 methyl-4-azabenzimidazole.

3. A process as defined in claim 1 wherein said second azabenzimidazoleis '6-methyl-4-azabenzimidazole.

4. A process as defined in claim 1 wherein said second azabenzimidazoleis 6-chloro-4-azabenzimidazole.

5. A process as defined in claim 1 wherein the mole ratio of saidS-hydroxy-4-azabenzimidazole to said second azabenzimidazole is fromabout 1:0.14 to about 1:20.

6. A process as defined in claim 1 which includes the steps ofdeveloping said exposed photosensitive element with an aqueous alkalinediffusion transfer processing composition; forming thereby an imagewisedistribution of image-forming components in said photosensitive element,as a function of the point-to-point degree of exposure thereof; andtransferring at least part of said imagewise distribution, by diffusion,to a contiguous imagereceiving layer to provide thereto a photographicdiffusion transfer image.

7. A process as defined in claim 6 wherein said imageforming componentscomprise color image-forming components.

8. A process as defined in claim 7 wherein said color image-formingcomponents comprise a dye which is a silver halide developing agent.

9. A process for forming transfer images in color, as defined in claim8, which includes, in combination, the steps of exposing aphotosensitive element which comprises at least two selectivelysensitized silver halide emulsion layers each having a dye ofpredetermined color associated therewith, which dye is a silver halidedeveloping agent and is soluble and diffusible in alkali; contactingsaid exposed photosensitive element with an aqueous alkaline processingcomposition; effecting thereby development of the latent imagescontained in each of said silver halide elements; immobilizing the dyeassociated with each of said emulsions as a result of development;forming thereby an imagewise distribution of mobile dye, as a functionof the point-to-point degree of exposure thereof; and transferring, byimbibition, at least a portion of each of said imagewise distributionsof mobile dye to a superposed image-receiving element to provide theretoa multicolor dye transfer image.

10. A process of forming transfer images in color, as defined in claim9, which includes, in combination, the steps of exposing aphotosensitive element comprising blue-sensitive, green-sensitive, andred-sensitive gelatino silver halide emulsion layers mounted on a commonsupport, said blue-sensitive, green-sensitive, and red-sensitive silverhalide emulsion layers having associated therewith, respectively,yellow, magenta, and cyan dyes, each of said dyes being a silver halidedeveloping agent soluble and difiusible in alkali; contacting saidexposed photosensitive element with an aqueous alkaline processingcomposition;

effecting thereby development of the latent image contained in each'silver halide emulsion; immobilizing said yellow, magenta, and cyandye, as a function of development of their respective associated silverhalide emulsion; forming thereby an imagewise distribution of mobileyellow, magenta, and cyan dye; and transferring, by imbibition, at leasta portion of each of said imagewise distributions of mobile dye to asuperposed image-receiving element to provide thereto a multicolor dyetransfer image.

11. A process as defined in claim 10 wherein said secondazabenzimidazole is 6-bromo-5-methyl-4-azabenzimidazole.

12. A process as defined in claim 10 wherein said secondazabenzimidazole is 6-methyl-4-azabenzimidazole.

13. A process as defined in claim 10 wherein said secondazabenzimidazole is 6-chlo ro-4-azabenzimidazole.

14. A process as defined in claim 10 wherein the mole ratio of said5-hydroxy-4-azabenzimidazole to said second azabenzimidazole is fromabout 1:0. 14 to about 1:20.

15. A process as defined in claim 10 wherein said anti foggantcomposition includes benzotriazole.

16. A process as defined in claim 10 wherein said process is conductedin the presence of imidazole.

17. As a product, a photosensitive element which comprises a supportlayer carrying a photosensitive silver halide emulsion having associatedtherewith an antifoggant composition comprising the combination of afirst azabenzimidazole consisting of 5-hydroxy-4-azabenzimidwherein R ishydrogen or a lower alkyl group; and R and R are each hydrogen, halogen,lower alkyl, nitro, lower alkoxy, aryl, sulfonamido, or carboxamidogroups.

18. As a product, a photosensitive element as defined in claim 17wherein said second azabenzirnidazole is 6bromo-5-methyl-4-azabenzimidazole.

19. As a product, a photosensitive element as defined in claim 17wherein said second azabenzimidazole is 6- methyl-4-azabenzimidazole.

20. As a product, a photosensitive element as defined in claim 17wherein said second azabenzirnidazole is 6- chloro-4-azabenzimidazole.

21. As a product, a photosensitive element as defined in claim 17wherein the mole ratio of said 5-hydroxy-4- azabenzimidazole to saidsecond azabenzimidazole is from about 1:0.14 to about 1:20.

22. As a product, a photosensitive element as defined in claim 17,wherein said silver halide emulsion has a dye, which dye is a silverhalide developing agent, associated therewith.

23. As a product, a photosensitive element as defined in claim 22,wherein said dye is disposed in a separate layer intermediate saidsilver halide emulsion and said support.

24. As a product, a photosenstive element as defined in claim 17,wherein said support layer carries on one surface at least twoselectively sensitized silver halide emulsion layers each having a dye,which dye is a silver halide developing agent, of predetermined colorassociated therewith.

25. As a product, a photosensitive element as defined in claim 24,wherein each of said selectively sensitized photosensitive emulsionlayers has predominant spectral sensitivity to separate regions of thespectrum and the dye associated with each of said emulsion layerspossesses a spectral absorption range substantially complementary to thepredominant sensitivity range of its associated emulsionlayer.

26. As a product, a photosensitive element as defined in claim 25,wherein said photosensitive silver halide emulsion layers comprise, insequence, a red-sensitive silver halide emulsion layer, agreen-sensitive silver halide emulsion layer, and a blue-sensitivesilver halide emulsion layer, having associated therewith, respectively,cyan, magenta, and yellow dyes, each of said dyes being silver halidedeveloping agents.

27. As a product, a photographic film unit as defined in claim 17,including a diffusion transfer image-receiving element affixed at leastone edge of said photosensitive element.

28. As a product, a photographic fihn unit as defined in claim 27including a rupturable container retaining an aqueous alkalineprocessing composition afiixed one edge of one of said photosensitiveand said image-receiving elements and adapted upon rupture to distributeits contents intermediate said photosensitive element and saidimagereceiving element upon super-positioning of said elements.

29. As a product, a photographic film unit as defined in claim 28wherein said antifoggant composition is disposed in said processingcomposition.

30. As a product, a photographic film unit as defined in claim 26including a diffusion transfer image-receiving element affixed at leastone edge of said photosensitive element and a rupturable containerretaining an aqueous alkaline processing composition containing saidantifoggant composition afiixed one edge of at least one of saidphotosensitive and said image-receiving elements and adapted uponrupture to distribute its contents intermediate said photosensitiveelement and said imagereceiving element upon super-positioning of saidelements.

31. As a product, a photographic film unit as defined in claim 30,wherein said second azabenzimidazole is 6-bromo-5-methyl-4-azabenzimidazole.

32. As a product, a photographic film unit as defined in claim 30,wherein said second azabenzimidazole is 6- methyl-4-azabenzimidazole.

33. As a product, a photographic film unit as defined in claim 30,wherein said second azabenzimidazole is 6- chloro-4-azabenzimidazole.

34. As a product,'a photographic film unit as defined in claim 30wherein the mole ratio of said 5-hydroxy-4- azabenzibidazole to saidsecond azabenzimidazole is from about 1:0.14 to about 1:20.

35. As a product, a film unit as defined in claim 30 wherein saidantifoggant composition includes benzotriazole.

36. As a product, a film unit as defined in claim 30 wherein saidprocessing composition includes imidazole.

References Cited UNITED STATES PATENTS 3,473,924 10/1969 Rogers 9633,377,166 4/1968 Weyerts, et al. 96-3 3,453,107 7/1969 Idelson 9632,353,754 7/1944 Peterson 96109 X NORMAN G. TORCHIN, Primary Examiner A.T. SURO PICO, Assistant Examiner US. Cl. X.R.

9629 D, 29 R, 48 HC, 56, 76 C, 77, 109

